The Bacillus genus comprises numerous endospore-forming bacteria that have myriad uses in the agricultural and animal nutrition fields, among others. Several strain of Bacillus are currently marketed for use as probiotics in animal feed as an alternative to antibiotics. These probiotics enhance animal health, including improving animal growth and feed efficiency, by modulating the gastrointestinal flora. Use of such probiotics has increased due to concerns about antibiotic residues in animal products for human consumption and the development of resistance to antibiotics. Work has been conducted in recent years to screen spore-forming bacteria for use as probiotics. Although various commercial products contain strains of Bacillus subtilis, Bacillus licheniformis, and Bacillus coagulans, such screening reveals that not all. Bacillus strains are effective feed additives.